1. Field of the Invention
This invention relates to a signal discriminator, and particularly to a signal discriminator which is attached to a cable for connecting electronic devices.
2. Discussion of the Background
Conventionally, as a device for absorbing noise which flows in a cable connected to an electronic device, and for preventing the noise from flowing into the electronic device, a device has been known which absorbs the noise by attaching a ferrite core which is a magnetic body, or the like around the cable.
FIGS. 20 and 21 are disclosed in Japanese Unexamined Utility Model Publication No. 13013/1987 (hereinafter the first conventional example).
In the first conventional example shown in FIGS. 20 and 21, a through hole is formed at the central portions of the ferrite cores 114 and 116 in the axial direction, and the cables 113 and 115 penetrate the ferrite cores.
In FIG. 20, a round cable is shown, and in FIG. 21, a flat cable is shown.
Furthermore, FIGS. 22 and 23 are disclosed in Japanese Unexamined Utility Model Publication No. 14770/1987 (hereinafter the second conventional example). The ferrite cores 118 and 120 are respectively divided in two in the axial direction, and respectively accommodated in the cases 117 and 119. In FIG. 22, an example of a round cable is shown, and in FIG. 23, that of a flat cable is shown.
Next, explanation will be given to the operation of the conventional examples using FIGS. 20 through 23.
Normally, when electric current flows in a cable, a magnetic field is generated around the cable, which varies with the frequency of the electric current. In order to absorb and eliminate unnecessary electric current other than signal current, a ferrite core is provided surrounding the cable, which has an impedance characteristic that passes the necessary signal and absorbs the unnecessary signal, thereby performing a filter action to absorb the unnecessary signal.
However, in FIGS. 20 and 21, the cable simply penetrates the ferrite core, and the attaching operationality thereof is not considered. Furthermore, in FIGS. 22 and 23, the divided ferrite cores are respectively accommodated in the cases 117 and 119 which are connected by a hinge, and the cases are latched simply by the resilience of the cases.
As stated above, since the conventional signal discriminator is constructed as above, in the signal discriminator of the first conventional example, the positioning attachment of the cable to the ferrite core is performed by using adhesive or a thermally contractive tube. Therefore many steps are required for the operation.
Furthermore, in the second conventional example, the contacting of the ferrite cores which are divided in the axial direction, is performed by pressure only due to the resilience of the cases. Therefore, in order to minimize magnetic reluctance of the cores, and to obtain a good filter characteristic, it is necessary to select the material of the cases and to prepare ferrite cores having high dimensional accuracy. Therefore the operation is complicated and necessitates high cost for the operation.
FIG. 35 is a perspective view of a conventional signal discriminator, (third conventional example) disclosed for instance, in Japanese Unexamined Utility Model Publication No. 133610/1985. In FIG. 35, a reference numeral 1 designates a ring-like magnetic core having the through hole 1a which the cable 2 penetrates. A numeral 3 designates a thermally contractive tube which fixes the magnetic core 1 to the cable 2, as well as protects the magnetic core 1.
Next, explanation will be given to the operation. When the magnetic core 1 is attached to the cable 2, one end of the cable 2 is disconnected from an electronic device to which the cable is connected, or from a connector or the like. The cable 2 is inserted into the through hole 1a of the magnetic core 1. The thermally contractive tube 3 is covered up on the magnetic core 1, and is contracted to secure the cable 2. After that, the end of the cable which is disconnected from the electronic device or from a connector or the like, is connected again to the electronic device or the connector as before.
FIG. 36 is an exploded perspective view of a conventional signal discriminator (fourth conventional example) utilizing divided magnetic cores, which is disclosed in Japanese Unexamined Utility Model Publication No. 91315/1990. In FIG. 36, a reference numeral 4 designates a divided magnetic core into which the magnetic core 1 is divided in the axial direction on the divided surface 1b, 5, a circular case which is fixed surroundingly around the cable 2, and which has the divided cases 5a and 5b, the hinge 6, the latches 7a and 7b, and the through holes 8a and 8b.
In the signal discriminator using the divided magnetic cores 4, the divided magnetic cores 4 are accommodated in the divided cases 5a and 5b of the case 5. The divided case 5a and 5b are closed and the latches 7a and 7b are connected, by which the case 5 is fixed to the cable 2, so that two divided magnetic cores 4 form a closed magnetic path around the cable 2. When electric current flows in the cable 2, the noise element of the signal is eliminated corresponding with the impedance characteristic of the magnetic core, and a necessary signal is discriminated.
Since the conventional signal discriminator is constructed as above, in the third conventional example shown in FIG. 35, when the signal discriminator is to be attached or detached, it is necessary to disconnect the cable 2 from a device or a connector to which one end of the cable 2 is connected. Furthermore it is necessary to exchange the thermally contractive tube 3.
On the other hand, in the fourth conventional example shown in FIG. 36, when the divided magnetic cores 4 are to be fixed to the cable 2, or are to be disconnected from the cable 2 , the divided magnetic cores 4 are easy to drop off from the case 5. Furthermore since the divided magnetic cores 4 are pressed by spring-like protrusions integrally formed with the case 5, it is necessary to enhance the dimensional accuracy of the divided magnetic cores 4, and to select the material of the case 5, to minimize the magnetic reluctance, and to obtain a good filter characteristic, which increases the cost of the signal discriminator.